The present invention relates to methods and apparatuses for recording and playing back video data, more particularly to a method and an apparatus for recording and playing back monitored video data, which will be suitable for recording video data for a long time for the purpose of monitoring and preventing of crimes.
Provided is a prior art time lapse VTR used as a video data recording device for recording video data from a video camera, suitable for monitoring and preventing crimes. Many of this type VTRs are improved from a home VHS VTR which is very popular at present to enable a long recording time. For example, in such a time lapse VTR, the magnetic tape can be fed at a ⅓ speed of the VHS Extended Play (EP) mode to record only one of the input video 3 fields on the tape. This enables extension of the recording time to 3 times that of the EP mode. Consequently, when a 120-min tape is used, the recording time is extended to 6 hours (120 minxc3x973) in the VHS EP mode. The recording time of the above time lapse VTR can thus be extended to 18 hours, 3 times that of the VHS EP mode. In this case, however, as understood clearly from the recording principle explained above, the number of fields per second is 20, which is ⅓ of the VHS (60 fields). In addition, audio signals can be recorded on audio tracks arranged in the longitudinal direction of the tape just like an ordinary VTR, but the tape speed becomes ⅓ of the normal one. As a result, the sound quality is degraded more than the normal one. In spite of this, the time lapse VTR can have an advantage of 18-hours of audio recording time.
Also proposed is an intermittent recording system for the above prior art time lapse VTR, in which system, the average tape speed is delayed and the number of recording fields is further reduced in order to extend the recording time. This system can have the maximum recording time of, for example 720 hours using a normal 120-min tape, by recording video data at a rate of 1 field per 2 seconds (120 fields) per frame (2 hoursxc3x973 timesxc3x97120=720 hours) In such a super-long time recording operation, the average tape feed speed is very slow. Thus, it becomes difficult to control the continuous feeding of the tape. To avoid this problem, the tape is fed intermittently in most cases and accordingly, it becomes impossible to record audio signals in audio tracks.
The conventional time lapse VTR ware opened in, for example, Examined Published Japanese Patent Application No. 3-12380, Examined Published Japanese Patent Application No. 7-63182, etc. The former patent report describes a method for controlling tape feeding so as to obtain the same recording tape pattern as that of the ordinary VTR even at the recording time by feeding the tape intermittently just like in the above-mentioned 720-hour recording. The latter patent report (No. 7-63182) describes a method for controlling the rotation speed of the cylinder to prevent generation of skew during intermittent recording.
As explained above, the time lapse VTR needs recording modes for continuous low speed tape feeding and intermittent tape feeding in addition to the normal continuous tape feeding, and a means for precisely controlling the capstan and the cylinder corresponding to those playback modes. In a recording operation, the same playback mode as each of those recording modes is needed to check pictures at the same speed as that of the recording. For this purpose, each of those prior art VTRs must be provided with various precision control means, so their prices become more higher than general home VTRs.
The time lapse art VTR cannot load (wind a magnetic tape onto the cylinder to which a magnetic head is attached to prepare for recording or playing back) a magnetic tape (video data recording medium) and unload (separate the tape from the cylinder) the magnetic tape within a short time, even for a recording operation in a recording mode for intermittent tape feeding. Therefore, the tape need to keep the loaded during recording. Further, since the cylinder has a large moment and requires a significant amount of time to stabilize its rotation speed, the cylinder must be rotated almost at a fixed speed continuously during the recording.
Therefore, the time lapse VTR must be kept loaded with a tape during recording of monitored video data and the cylinder is, rotated continuously. Especially, in the above super-long recording mode (720-hour mode), the VTR has a disadvantage that because the cylinder is kept rotated in contact with the tape for 720 hours, the tape is damaged far more rapidly than when used for a home VTR. In the same way, because the head is in contact with the tape, the head is also worn rapidly. The mechanisms such as the motor and belt used for making the cylinder rotate are also degraded rapidly and often damaged, since they are running for a long time respectively.
Further, conventional helical scanning VTR also has a following defect; the recording track pattern angle on the tape loaded is decided by both the rotation speed of the cylinder and the feed speed of the tape, so that the track pattern recorded at the above slow speed tape feeding or the tape stops has an angle that is different from the normal speed tape feeding. Therefore, when playing back the track pattern recorded in such way, a mismatching occurs between the tracing angle of the head and the angle of the track pattern, causing the S/N (signal-noise ratio) to be degraded in a part of the playback signals. As a result, the quality of output pictures is significantly lowered.
It is an object of the present invention to provide a method and an apparatus for recording and playing back monitored video data, which can store video data on a magnetic tape for a period long enough to be used for monitoring and preventing crimes, etc. In addition, in the apparatus, there is no need to record video data while the recording head is in contact with the magnetic tape for a long time and while the recording head is moved, without special mechanisms for intermittent feeding, etc. In other words, a general home VTR can also be used to store video data on a magnetic tape for a period long enough to monitor and prevent crimes, etc.
It is another object of the present invention to solve the above-mentioned problems of conventional time lapse VTR and provide an apparatus for recording and playing back video data, which can improve its mechanical reliability and extend the life of the magnetic tape in use by reducing the operating time of the parts that are apt to wear and be damaged, without employing any high precision control means for intermittent tape feeding.
It is a further object of the present invention to provide an apparatus for recording and playing back video data, which can output good quality playback images without degrading the playback signals even in a different tape-speed mode from the recording mode.
In order to achieve the above objects, according to the present invention, video data compressed on the time axis is stored on a magnetic tape, so that when video signals from a monitoring video camera are to be stored on the magnetic tape continuously for a long time, the magnetic tape recording apparatus is operated for a period shorter than the monitoring period. Thus, it is not required to operate the magnetic tape recording device (VTR) continuously during the monitoring.
In other words, the present invention provides a method for recording and playing back monitored video data for storing video signals, generated continuously for a long time, on a magnetic tape; wherein while continuously generating video signals for a long time and entering such video signals and compressing it on the time axis, the compressed video signals are then being output as digital video data and recorded on a magnetic tape, so that the digital video signals are stored on the magnetic tape for a period shorter than the period in which the video signals are generated continuously.
Furthermore, the present invention provides an apparatus for recording and playing back monitored video data and storing video signals generated continuously for a long time on a magnetic tape, comprising a means of generating video signals continuously for a long time; a means of entering video signals generated by the video signal generating means continuously for a long time and compressing the video signals on the time axis so as to be output as digital signal video data; and a means of recording and playing back digital video data from the time axis compressing means on a magnetic tape, wherein the period in which the magnetic tape recording means records digital video data on the magnetic tape is shorter than the period in which the video signal generating means generates video signals continuously.
In order to achieve the above objects, the monitored data recording and playback apparatus provided by the present invention for recording video information for a long time, comprises the first memory means of storing video data temporarily; the first recording and playback means of recording the data output from the first memory means on a recording medium; the second memory means of storing playback data from the first recording and playback means temporarily; the second recording and playback means of recording data output from the second memory means on a magnetic tape by forming oblique tracks on the magnetic tape; and a control means of controlling the write and read operations of the first and second means and recording and playback operations of the first and second recording and playback means. The control means controls so that reading from the first memory means and recording by the first recording and playback means are repeated each time the first specified data amount is reached, as well as controls the first recording and playback means and the second recording and playback means in the first operation mode so that they stop recording and playback operations, respectively this continues until the data recorded in the first recording and playback means and not played back yet reaches the second specified data amount, which is greater than the first specified data amount. In addition, the control means controls the first and second recording and playback means so that when the data recorded and not played back yet reaches the second specified data amount, the first recording and playback means time-shares recording and playback of data until the data of the second specified data amount is played back completely. Furthermore, the control means controls so that the second recording and playback means records the data read by the second memory means at a specified transfer rate on a magnetic tape fed continuously while forming oblique tracks on the tape and feeding the tape continuously.
Furthermore, in order to achieve the above objects, the recording and playback apparatus provided by the present invention comprises: the first memory means of storing video data temporarily; the first and second recording and playback means of recording the data output from the first memory means on a recording medium; the second memory means of storing playback data from the first and second recording and playback means; the third recording and playback means of recording the data output from the second memory means on a magnetic tape by forming oblique tracks on the tape; and a control means of controlling write and read operations of the first and second memory means and recording and playback operations of the first, second, and third recording and playback means, so that when in recording of video data, the control means controls so that four operation modes are changed appropriately as follows according to the data amount to read and the data amount to play back in the first and second recording and playback means; in the first operation mode, the control means controls so that reading of video data from the first memory means and recording by the first recording and playback means are repeated each time the first specified data amount is reached and recording and playback operations of the second and third recording and playback means are stopped. In the second operation mode, the control means controls so that reading of video data from the first memory means and recording by the second recording and playback means are repeated each time the first specified data amount is reached and the video data read from the firs recording and playback means is stored in the second memory means temporarily, and then video data is read from the second memory means at a specified transfer rate while the third recording and playback means is enabled to record transferred data on the magnetic tape by forming oblique tracks on the tape. In the third operation mode, the control means controls so that reading of video data from the first memory means and recording by the second recording and playback means are repeated each time the first specified data amount is reached while recording and playback operations of the first and third recording and playback means are stopped. Lastly, in the fourth operation mode, the control means controls so that reading of video data from the first memory means and recording by the first recording and playback means are repeated each time the first specified data amount is reached, and video data read from the second recording and playback means is stored in the second memory means temporarily, and then video data is read from the second memory means at a specified transfer rate while the third recording and playback means is enabled to record transferred data on the magnetic tape fed continuously by forming oblique tracks on the tape.
Furthermore, in order to achieve the above objects, the monitored video data recording and playback apparatus provided by the present invention, which records compressed and encoded video data on a magnetic tape by forming oblique tracks on the tape, is further provided with a means of changing the time order of video data when in a recording operation so that only the first group video data selected from the above video data and compressed and encoded in the m (m=an integer of 2 or over) frame time interval is continued by n (n=an integer of 2 or over) frames; a means of restoring the initial video data time orders of the first group video data and other video data; a means of controlling so as to play back only the first group video data selectively and feed other data fast; and a memory means of storing the played-back first group video data temporarily. These and other features of the invention that will be apparent to those skilled in the art from the following detailed description of the invention, taken together with the accompanying drawings.